Manganese-boron alloy



Patented Sept. 6, 1938 UNITED STATES PATENT OFFICE No Drawing. Application January 21, 1937, Serial No. 121,610

1 Claim.

This invention relates to a new alloy steel and relates particularly to an alloy steel containing manganese, boron and nickel.

An object of this invention is to supply a 5 manganese alloy steel which has materially higher hardness and greater resistance to abrasion and impact than heretofore known manganese steels. Furthermore, the new alloy may be readily repaired or rebuilt by welding with no adverse effects on the physical properties of the parent metal.

Cast manganese steel, commonly termed Hadfield steel, contains from 10% to 14% manganese and more-than 1% carbon. This steel is ex- 15 tremely brittle in the cast condition due to the presence of free carbides of iron and manganese. Heat treatment is necessary to change the structure of the steel and develop the required tensile strength and toughness. Such heat treated steel above maximum the outer layer of the metal be-' comes so brittle that it flakes or chips oil, ex- I posing metal of appreciably lower hardness. Therefore, the degree of resistance to abrasion 30 of such steel depends largely upon the amount of work hardening to which it has been subjected. It is known that manganese steel does not have as high resistance to abrasion as various other hard alloys.

85 One of the most serious defects of heretofore known manganese steel is that by reason of the high ductility of the metal it undergoes plastic deformation under stress and becomes set in the deformed shape.

40 All of the heretofore known manganese steels are diflicult to weld. The high temperatures of the welding operation destroys the austenitic structure in a zone adjacent to the weld and the metal in that area is embrittled.

45 A steel containing from 2% to 10% nickel, in addition to the usual amounts of manganese and carbon, has been proposed in an attempt to overi come some of the difllculties of welding manganese steel. In this case nickel functions to form 50 a more stable solid solution of iron and manganese carbides in the iron matrix, and thus inhibit the precipitation of free carbides when the steel is allowed to cool at a normal rate from elevated temperatures. It has been found, how- 55 ever, that the presence of an effective amount of nickel also acts to greatly retard surface hardening of the steel under cold work. The maximum hardness developed in such nickel containing steel neverexceeds and is usually less than the. maximum hardness developed in the Hadfield 5 type. Consequently, manganese steel containing. nickel doesnot resist abrasion as well as ordinary manganese steel.

I have discovered that an alloycontaining manganese from approximately 6.25% to 16%, 10 boron 0.25% to 1.75%, nickel 0.50% to 10% and the balance substantially iron has materially higher hardness and greater resistance to abrasion than previously known manganese steels.

One distinct advantage of the alloy of the 16 present invention is that it may be used for a wide variety of industrial purposes, including parts of equipment, in the cast condition. The cast metal has a minimum hardness of from 550 to-650 Brinell and this can be increased from 75 to 200 20 BHN by cold work, i. e.-impact.' The tensile strength of my alloy is, in general, superior to that of heat treated manganese steel of the previously known types. The alloy of the present invention is characterized by somewhat lower ductility than that of previously known manganese steels and is not subject to excessive plastic deformation. By reason of the distinctive physical structure, the present alloy has from three to seven times greater resistance to abrasion and impact than other manganese steel.

The outstanding advantages of my alloy are due to the presence of appreciable and effective amounts of boron. Carbon is not an essential component of my alloy, but by reason of the fact that varying amounts of carbon are usually present in commercial grades of materials used in producing the alloy I find that it is desirable to allow 'for the inclusion of a small percentage of carbon. I usually prefer to limit the maximum 40 carboncontent to approximately 0.40%. I have found, however, that when the alloy contains carbon up to approximately 0.85% that no free carbides, or other brittle and harmful segregates are found in the structure of the cast or welded material, regardless of the rate of cooling.

I have further found that the hardness, abrasion resistance and other physical properties and characteristics of my alloy can be varied over a considerable range by means of thermaltreatment. I have found, for example, that by heating the alloy to a temperature of approximately 1100 C., or somewhat higher, for a period of time, followed by quenching, that the structure consists of substantia'iy a solid solution. Bodies oi the alloy which have been subjected to such methods of heat treatment have much greater resistance to abrasion and impact than heretofore known manganese steels.

It will be apparent from the foregoing that the composition and physical structure of the manganese-boron-nickel steel is markedly different from the compositions and structures of heretofore known manganese steels.

The alloy of the present invention has a high degree of weldability, that is, castings or other forms of the alloy may be surfaced or rebuilt to original dimensions'with weld rods having substantially the same composition, or materially difierent compositions.

Examples of my alloy which I have found to be valuable for wearing parts of equipment and other uses are manganese 9.75%, boron 0.70%, nickel 0.75%, carbon 0.15% and the balance substantially iron; manganese 12%, boron 0.80%,

nickel 1.75%, carbon 0.30% and the balance substantially iron; manganese 14%, boron 1.10%, nickel 2.20%, and the balance substantially iron.

The alloys of the present invention comprise m n anese 6.25% to 1 boron 0.25% to 1.75%, nickel 0.50% to 10%, carbon, when present, not exceeding a maximum of 0.85% and the balance substantially iron.

It will be understood that the alloy will usually contain fractional percentages of impurities incidental to manufacture, such for example as silicon, sulphur and phosphorus.

' Subject matter disclosed herein but not claimed is claimed in my co-pending application, Serial No. 160,780, filed August 25, 1937.

I claim:

An alloy characterized by relatively high resistance to deformation and abrasion containing manganese 6.25% to 16%, boron 0.25% to 1.75%, nickel 0.50% to 10%, carbon not exceeding a maximum of 0.85% and the balance iron.

ANTHONY G. on GOLYER. 

